1. Field of the Invention
This invention relates to an insecticide composition. More particularly it relates to a controlled release foliar insecticide composition. This invention especially relates to a controlled release composition containing an organo-thiophosphate insecticide, Imidan.
2. Description of the Prior Art
Foliar insecticides can be broadly classified by the manner in which they provide effective control. Some insecticides are toxic as contact poisons, e.g., they are lethal to insects by being brought in contact therewith as when an insect lights onto or crawls on foliage coated with the insecticide. Others prove lethal to insects as a stomach poison when the insect ingests insecticide-coated foliage.
The farmer's goal is to realize the highest possible return on his investment. Therefore, maximizing the yield of the marketable commodity is of prime concern. Apart from the proper use of fertilizers, adapted varieties and proper cultural practices, the farmer depends on crop protection chemicals to maximize yield. While the rationale for their use against weeds, diseases and insects is obvious, there are a number of associated disadvantages. These include such factors as toxicity, residuality, cost, resistance by pests, and weatherability. These factors are somewhat interrelated and in recent years, attempts have been made to deal with them.
Improving the efficiency of foliar insecticides can be achieved by reducing the application rates or by reducing the number of applications. The classical objective of controlled release technology is to extend the longevity of a pesticide thereby leading to decreased use and increased benefit to both the farmer and the consumer. Controlled release of a foliar insecticide is one effective means of reducing the per acre cost of the insecticide. Not only are the number of applications reduced but effectiveness of the insecticide is increased and undesirable side-effects to beneficial-insects often minimized through reduced run-off and reduced spray drift.
Although the field of controlled release technology has been practiced for a number of years in the pharmaceutical industry, it is only recently that active interest has been displayed in the use of this technology for agricultural pesticides.
In one application, an interfacially polymerized microcapsule product containing methyl parathion has been utilized on cotton plants. In another, a laminate containing pesticide sandwiched between layers of plastic film has been applied to agricultural systems. (Proceedings of the Controlled Release Pesticide Symposium (1976).)
U.S. Pat, No. 3,212,967 to McFadden et al. discloses biocidally-active phosphorothioate esters which are polymerized with ethenoid monomers, such as acrylates, methacrylates and the like to form unitary polymeric molecules having the biocidal component temporarily held therein. The biocidal component is slowly released from the polymeric material in which it is entrapped when the materials are employed as film-forming coatings. These biocidally-active organic, polymeric materials are applied as aqueous latex dispersions or organic solvent solutions.
U.S. Pat. No. 3,592,910 to Clark et al. is directed to the use of liquid polyterpenes to protect pesticides against weathering and to extend the residual life of the pesticide. Pesticides, including insecticides, are controlled by release from these formulations. The polyterpene-containing composition may be applied to plants in undiluted condition, as a water emulsion or an organic solvent solution. This patent also states that acrylic polymers, vinyl-acrylic copolymers and other resins have been used as sticking agents for pesticides. However, no improved biological efficacy was reported for any of these compositions.
U.S. Pat. No. 2,767,194 to Fancher discloses a number of monothio- and dithio-phosphates and their method of preparation. These products are useful as insecticides and acaracides. One particularly effective dithio-phosphate is N-(mercaptomethyl) phthalimide-S-(O,O-dimethyl phosphorodithioate) which is also known as Imidan. These compounds were effective when acetone solutions thereof were dispersed in water with surfactants and applied as a spray.
Imidan is primarily used for the control of insects that attack commerical farm crops, especially fruit crops. The insects which are effectively controlled by Imidan include alfalfa weevil, apple maggot, coddling moth, grape berrymoth, green apple aphid, Mexican bean beetle, oriental fruit moth, plum curculio, redbanded leafroller, rosy aphid, tobacco hornworm and tobacco budworm. The commercial cash crops treated with Imidan include such fruit crops as apples, apricots, cherries, grapes, nectarines, peaches, pears, plums and strawberries, as well as alfalfa, almonds, beans, citrus, corn, peas, pecans, potatoes, tobacco, rice and the like. Sales of Imidan in 1976 for use on apple orchards alone constituted over two million dollars and amounted to over four million dollars for use on all fruit crops.
Imidan is a white crystalline solid and is available commercially in technical grade purity of 94-96%. (All percentage figures herein are in terms of weight unless stated otherwise.) It is also available as a 50% active wettable powder. Imidan has been applied to cash crops as a foliar insecticide in the form of an aqueous spray. In this form, the adhesion to leaf surfaces, particularly if they are dirty or dusty, is not good and the weathering from rainfall requires repeated applications.
It has been discovered and disclosed in related patent application Ser. No. 358,125 that a controlled release insecticide composition can be prepared in the form of an emulsifiable concentrate which contains Imidan, an acrylic resin, a surfactant and an organic solvent in which all of the ingredients are soluble. By employing the Imidan in its technical grades or in its pure crystalline form, this composrtion is insecticidal to foliage eating or chewing insects susceptible to stomach poisons while leaving insects susceptible to contact poisons essentially unaffected.
It is an object of the invention to increase the efficacy of Imidan by increasing its retention on leaf surfaces and increasing its weatherability, specifically against rainfall stress.
It is another object of this invention to provide Imidan in a controlled release formulation.
It is still another object of this invention to provide Imidan in a manner which reduces the frequency of application.
It is still a further object of this invention to provide a means of applying Imidan to foliar substrates whereby the runoff of the insecticide to the surrounding environment is substantially reduced.